Bus Plugs Frequently-Asked Questions

Click on question marks below to get answers to these frequently-asked questions.

Where are bus plugs used?

Bus plugs, or bus duct switches, are used in manufacturing and industrial plants to distribute power in a convenient accessible way about the facility. Electrical bus plugs are used with busway to quickly tap feeders off the busway for power to panels, production equipment, and motors.

Why are bus plugs used?

Bus duct with bus plugs or bus switches allow the easy addition or relocation of production equipment. The electrical feeder to a machine can simply be relocated to another bus plug in the bus duct. And it is easy to add a bus plug or bus switch to bus duct or bus way.

What are the dangers of bus plugs and bus switches?

Bus plugs are an effective switching mechanism, but can be very dangerous to install or remove from an energized bus duct.

Do all bus plugs have fuses in them?

No, some bus plugs have circuit breakers and some have fused switches.

We just relocated a bus plug. This bus plug has a circuit breaker in it. My electrician recommended replacing this bus plug with one having fuses instead of a circuit breaker. He said fuses were quicker. I though he was joking, giving me the ‘run around’ so to speak. Anyway, he was serious and said something about less arcing if something went wrong. What’s he talking about? We don’t have just one bus plug, we have about 75. This could cost $1000’s.

Fuses in a bus plug will interrupt an electrical fault much faster than a circuit breaker. Therefore a fused bus plug will limit the amount of electrical arcing during a fault better than a circuit breaker. A bus plug with a circuit breaker may take 25 times as long to interrupt a fault than a bus plug with fuses. A bus plug with a breaker may take 1/10th of a second to interrupt a fault. A bus plug with fuses might only take 1/240th of a second. This is a tremendous difference during an arc flash. See Arc Flash Hazards or NFPA 70E. But there is one advantage using a circuit breaker. When a circuit breaker trips, it opens all three phases. A fused bus plug might “single phase,” ie blow just one or two fuses of the three fuses. Motors can be damaged by “single phasing.” So a bus plug with fuses may protect people better than a bus plug with a circuit breaker. But a bus plug with breakers may protect motors better.

Does MIDWEST Switchgear Division offer bus plugs (buss plugs)?

Yes, you can purchase a new or reconditioned bus plug (buss plugs) from us.

What is the difference between busway and bus duct?

They are the same. Bus duct is the term used by electricians and contractors. Busway is the term typically used by the manufacturers. People that use the stuff call it bus duct.

Does Midwest Switchgear sell bus plugs which are not re-conditioned?

Typically not. Unless the bus plug has not been in service at all, we prefer from an engineering and quality control point of view to recondition the bus plug before allowing it to go out the door. This ensures the customer the maximum performance to be expected from the bus plug.

Should we first de-energize the entire Bus Duct before we install and remove Bus Plugs?

Yes, that would be a very good work practice but often that is not the case in the real world. Bus Duct was designed as a mechanism to remove and install tap points along a physical length of insulated live bus to allow flexibility in the workspace so that machine relocation that can be implemented quickly as production needs change. Too often we hear that many do this work with the duct energized.
Adding a small bus plug sized at 30 amps, fused at 15 or 20 amps to feed a small machine may mask the fact that that bus plug is being connected to a live bus that is rated for considerably more amps than the 15 or 20 amps you are trying to send to a machine.
The logistics of handling something from a ladder or man bucket and trying to engage the bus plug stabs onto the energized three phases, spaced only a few inches apart, appears to be asking for trouble.

Why do bus plugs have such a short life expectancy?

Bus plugs like stand up comics are often subjected to harsh environmental conditions. The atmosphere in many facilities contain contaminants which are hard on bus plugs. Oil and heat from manufacturing facilities can be party spoilers on bus plug longevity. For more information on this aspect see our article called “Plugging Away”.

Can a 30 amp fused bus plug be swapped out for a 60 amp bus plug in a pinch to get needed equipment up and running until a 60 amp bus plug can be found and installed if 60 amp fuses are temporarily installed in the 30 amp bus plug?

Lets take that one step at a time. Regarding the first part of your question: The answer to that would be a qualified yes and no. Typically a 30 amp bus plug can be swapped out for a 60 amp bus plug, but with one huge caveat. If we look at a Square D PQ3603 (30 amp) and a PQ 3606 (60 amp) for example, the physical dimensions of these two bus plugs are the same, with the exception of the fuse clip size. So to answer the second part of your question, 60 amp fuses will not fit in 30 amp fuse clips. However, the 30 amp bus plug could be used in place of the 60 amp bus plug if the load of the circuit is less than 30 amps. Would we recommend doing this. This question asks whether there is justification to change the circuit from the original 60 amp spec to a 30 amp spec. This could only be determined by performing a careful load analysis of the circuit.